A method and an arrangement for reducing the toxic substances in combustion exhaust gases wherein a gas having an increased oxygen content is supplied to the inducted air is disclosed, for example, in U.S. patent application Ser. No. 08/682,593, filed Feb. 2, 1996, and incorporated herein by reference. The oxygen-enriched gas is obtained in that air is guided through a membrane which is permeable only for oxygen molecules and is mounted in a chamber
With this kind of an oxygen enrichment of the air supplied to the engine, the exhaust-gas temperature is increased and therefore the start time of the catalytic converter is reduced. This start time is that time which elapses before the catalytic converter reaches its operating temperature and its full operational effect. At the same time, the fuel conversion in the engine is improved so that the raw emissions of carbon monoxide and hydrocarbons (CO, HC) are reduced. Furthermore, the nitrogen content during combustion is reduced whereby less nitrogen oxide is produced which must be catalytically converted to reduce the burden to the environment.
In a method and an arrangement of this kind, it is problematical that the oxygen content of the oxygen-enriched gas (which is supplied to the intake air) cannot be exactly determined so that, for example, an exact control of the combustion processes is not possible by means of an engine control known per se. Rather, the control must take place indirectly, that is, by known sensor means and engine controls which, however, requires a considerable intervention into the control algorithms of the engine control.
An arrangement for controlling an exhaust-gas feedback is disclosed in U.S. Pat. No. 4,905,564. In this arrangement, the control of the fed-back exhaust gas is made possible via an exhaust-gas feedback valve. In this arrangement, an oxygen probe is provided which detects the oxygen content in the intake channel. An internal combustion engine is controlled in dependence upon the detected sensor signal. An arrangement of this kind does not make possible the control of the oxygen content. Furthermore, the arrangement does not make possible an oxygen enrichment because the fed-back exhaust gas contains less oxygen than the usual inducted air. Such an exhaust-gas feedback serves essentially to reduce the nitrogen oxide (NO) as known per se which is effected in that the fed-back exhaust gas (that is, an inert gas) is admixed to the inducted air. In this way, the combustion temperature is reduced and less nitrogen oxide is generated. A reduction of the toxic emission while simultaneously increasing the power of the engine is not possible with an arrangement of this kind.